Australia's 7,686,850 km² (2,967,909 mi²) landmass is on the Indo-Australian Plate. Surrounded by the Indian, Southern and Pacific oceans, Australia is separated from Asia by the Arafura and Timor seas. Australia has a total 25,760 km (16,007 mi) of coastline and claims an extensive Exclusive Economic Zone of 8,148,250 km² or 3,146,057 mi² (excluding the Australian Antarctic Territory). Climate is highly influenced by ocean currents, including the El Niño southern oscillation, which is correlated with periodic drought, and the seasonal tropical low pressure system that produces cyclones in northern Australia.

By far the largest part of Australia is desert or semi-arid. Australia is the driest inhabited continent, the flattest, and has the oldest and least fertile soils. Only the south-east and south-west corners of the continent have a temperate climate. The northern part of the country, with a tropical climate, has a vegetation consisting of rainforest, woodland, grassland and desert. The Great Barrier Reef, the world's largest coral reef, lies a short distance off the north-east coast and extends for over 2,000 km (1,250 mi). The world's two largest monoliths are located in Australia, Mount Augustus in Western Australia is the largest and Uluru in central Australia is the second largest. At 2,228 m (7,310 ft), Mount Kosciuszko on the Great Dividing Range is the highest mountain on the Australian mainland, although Mawson Peak on the remote Australian territory of Heard Island is taller at 2,745 m (9,006 ft).

Although most of Australia is semi-arid or desert, it covers a diverse range of habitats, from alpine heaths to tropical rainforests. Because of the great age and consequent low levels of fertility of the continent, its extremely variable weather patterns, and its long-term geographic isolation, much of Australia's biota is unique and diverse. About 85% of flowering plants, 84% of mammals, more than 45% of birds, and 89% of in-shore, temperate-zone fish are endemic. Many of Australia's ecoregions, and the species within those regions, are threatened by human activities and introduced plant and animal species. The federal Environment Protection and Biodiversity Conservation Act 1999 is a legal framework used for the protection of threatened species. Numerous protected areas have been created to protect and preserve Australia's unique ecosystems, 64 wetlands are registered under the Ramsar Convention, and 16 World Heritage Sites have been established. Australia was ranked 13th in the World on the 2005 Environmental Sustainability Index.

Most Australian plant species are evergreen and many are adapted to fire and drought, including the eucalypts and acacias. Australia has a rich variety of endemic legume species that thrive in nutrient-poor soils because of their symbiosis with Rhizobia bacteria and mycorrhizal fungi. Well-known Australian fauna include monotremes (the platypus and echidna), and a host of marsupials, including the koala, kangaroo, wombat, and birds such as the emu, cockatoo, and kookaburra. The dingo was introduced by Austronesian people that traded with Indigenous Australians around 4000 BCE. Many plant and animal species became extinct soon after human settlement, including the Australian megafauna; many more have become extinct since European settlement, among them the Thylacine (Tasmanian Tiger).

The continent of Australia has been inhabited for over 40,000 years by Indigenous Australians. After sporadic visits by fishermen from the north and by European explorers and merchants starting in the 17th century, the eastern half of the continent was claimed by the British in 1770 and officially settled as the penal colony of New South Wales on 26 January 1788. As the population grew and new areas were explored, another five largely self-governing Crown Colonies were successively established over the course of the 19th century.

On 1 January 1901, the six colonies federated and the Commonwealth of Australia was formed. Since federation, Australia has maintained a stable liberal democratic political system and remains a Commonwealth Realm. The current population of around 20.4 million is concentrated mainly in the large coastal cities of Sydney, Melbourne, Brisbane, Perth and Adelaide.

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